Vacuum cleaning systems for large remote areas (such as flat roofs) have been proposed in the art, and generally such equipment is exemplified by many patents. Such patents as U.S. Pat. No. 3,955,236, dated May 11, 1976; U.S. Pat. No. 3,842,461, dated Oct. 22, 1974; U.S. Pat. No. 3,404,776, dated Oct. 8, 1968; U.S. Pat. No. 2,772,438, dated Dec. 4, 1956; U.S. Pat. No. 3,594,848, dated July 27, 1971; German Pat. No. 631,580, dated June 24, 1936; French Pat. No. 830,876, dated May 23, 1938, among many others, show heavy duty vacuum cleaning systems for such as flat roof cleaning, road cleaning, and the like. The vacuum cleaning systems are used for various purposes, and the systems using large lines, 4 inch flexible tubes and greater, are the systems to which the invention relates. When vacuum cleaning systems are used for generally flat roofs (of the tar and gravel type) the cleaning apparatus must be capable of handling large volumes of heavy material, namely gravel and dirt, and large volumes of very fine dust. The fine dust has been deposited on such roofs as a wind born dust over the years that the roof has been in existence. When disturbed, this fine dust is easily air entrained, penetrates buildings, vehicles and all structures and areas in the vicinity of the roof being cleaned. This causes conventional cleaning methods to be extremely dirty and messy for the entire surrounding area.
The handling of dirty gravel and large volumes of dust is a major materials handling problem. Many of the vacuum systems that have been developed to handle such gravel and dust utilize enclosed containers so as to maintain a clean area in the vicinity of the roof re-roofing procedures. A majority of the prior art units are self contained units which include the vacuum system, filters and separators and container for the debris, and the transportation prime mover or truck for the unit.
The prior art devices have many different ways of containing the gravel and dust, but the most frequently used is a container mounted on a truck with an integral air pump and filtering system. All are arranged to dump the container, filled with the picked up gravel and dust. The arrangement is apparently satisfactory for many purposes, particularly for small jobs which can be completed without completely filling the single container.
Thus such arrangements are not very efficient when used on large jobs having gravel and dust loads considerably larger than the single container. This is so because the entire unit must be driven to the dump for emptying the containers. This obviously reduces working time on the roofing job itself thus providing an economic deterrent. Also, substantial capital is tied up in the truck unit having the mounted container and the vacuum equipment, since this limits the usefulness of the truck or prime mover.